Read-out and transmission of electrostatic information presentations



June 7, 1966 L. E. WALKUP 3,255,308

READ-OUT AND TRANSMISSION OF ELECTROSTATIC INFORMATIQN PRESENTATIONS Filed Nov. 19, 1.962 3 Sheets-Sheet 1 SCANNING SYNCH SAWTOOTH 4-' PULSE 2| b GENERATOR SEPARATOR f 4 33 34 22 25 SYNCH PULSE 36 23 $1 T GENERATOR SYNCH PULSE GENERATOR 6| SYNCH I PULSE SEPARATOR SCANN'NG SAWTOOTH Ki GENERATOR 63 INVENTOR. LEWIS E. WALKUP ha 3&1

A T TORNEY June 7, 1966 L. E. WALKUP 3, 5 3 8 READ-OUT AND TRANSMISSION OF ELECTROSTATIC INFORMATION PRESENTATIONS Filed Nov. 1.9, 1962 3 Sheets-Sheet 2 ELECTROSTATIC lALPHA-NUMERIC INFORMATION IMPRINTER OUTPUT Fig.2

5s\ WEB PRECONDITIONER LEWIS E. WALKUP w g Q ATTORNEY June 7, 1966 1.. E. WALKUP 3,255,308

READ-OUT AND TRANSMISSION OF ELECTROSTATIC INFORMATION PRESENTATIONS Filed Nov. 19, 1962 3 Sheets-Sheet 6 PRECHARGING STATION READ-OUT STATION OPTICAL IMAGE READ-IN STATION 73 I H i I l l 76 760 D OUTPUT 76b 77 78 80 Fig. 4

INVENTOR. LEWIS E. WALKUP A 7' TOPNEV United States Patent 3,255,308 READ-OUT AND TRANSMISSION OF ELECTRO- STATIC INFORMATION PRESENTATIONS Lewis E. Walkup, Columbus, Ohio, assignor to Xerox Corporation, Rochester, N.Y., a corporation of New York Filed Nov. 19, 1962, Ser. No. 238,384 3 Claims. (Cl. 1786.6)

The present invention relates to the art of information transmission, and particularly to the transducing of information presented in a two dimensional space domain into a time domain electrical signal adapted to be transmitted to a remote station for reconversion into the two dimensional space domain, to reproduce the information in -a form similar or related to its original presentation.

The information transducing aspect of the present invention relates primarily to the sensing of a spatially arranged electrostatic information pattern, and the conversion of this information into an electric current form capable of transmission to a remote station. At the remote station, the information can be reconverted into a spatial presentation of any one of various forms, one of which is a reconversion to its original electrostatic pattern.

, Information may be converted to and presented in electrostatic form in various known ways. One way employs a technique widely used in xerography, and in volves the use of a selenium or other photoconductive insulating plate. Basically, the plate is first conditioned by application of a uniform electrostatic charge thereto, and then exposed to an optical image of the information to be presented. The charge on the plate is selectively diminished or depleted by leaking off the plate in accordance with the illumination intensity pattern, thereby providing an electrostatic presentation of the optical information. A second way of establishing an electrostatic record of information is to expose a web of dielectric film material to electrical ion field discharge from an array of electrodes. The electrodes may be either point electrodes, parts of an alphanumeric character composite, or the like. In this approach, usually the electrodes are selectively energized in a prescribed sequence or selection while the web is moved past the array of electrodes. Electrostatic charges are created on .the web in accordance' with the energization of the electrodes, thereby establishing an electrostatic pattern of information on the web. Still another way of establishing an electrostatic pattern is to employ a cathode ray pin tube in conjunction with a web of dielectric film material. The pin tube is a cathode ray type tube wherein the target area for the-cathode ray beam comprises an array of electrically conductive pins which pass through the tubes target wall. These target pins are scanned by the beam sequentially, and as each pin is bombarded by the beam, its potential is raised to effect an electric field discharge from that pin to that increment of dielectric web momentarily located immediately opposite and adjacent the exterior end of the pin. In this manner, as the web is moved past the pin array, a pattern of varying densities of electrostatic charges is created thereon in accordance with the varying intensity of the cathode ray beam as controlled by the tubes control grid.

These various known approaches for establishing an electrostatic record of information are explained in detail in the following patents and patent applications, cited for purposes of example, and not by way of limitation on the present invention: Carlson US. Patent 2,297,- 691; Walkup US. Patent 2,825,814; and pending application Serial No. 532,534, filed September 6, 1955, to Carlson. v

The primary concern of the present invention is the Patented June 7, 1966 read-out of electrostatic information patterns and the conversion there-of to electrical current form, along with the. transmission of this converted information to a remote station and the reconversion thereof to a spatial record form.

The read-out of electrostatic information patterns and conversion thereof to electric current values is accomplished in accordance with one embodiment of the present invention bymeans of a cathode ray pin tube of the character hereinabove referred to. A web, plate, or other dielectric medium carrying an electrostatic charge pattern is passed in close proximity to the target face of a pin tube while the pins are scanned by the cathode ray beam controlled to have a constant intensity, and this intensity is made sufficient to effect an electrical field discharge in the air gap between each pin as it is energized and the immediately adjacent respective area of the dielectric medium carrying the electrostatic information pattern. This field discharge effects an ion current flow between the energized pin and its said respective dielectric medium area. However, this ion current flow is modulated or controlled by the potential difference existing between the pin and its said adjacent dielectric medium area, which of course is a function of the information charge present on said dielectric medium area. A conductive plate backs the dielectric medium in the area immediately opposite the target pins of the pin tube, and this backing plate is included in the electrical return path of the cathode ray beam to its cathode. Thus, as the pins are scanned, and each is successively energized by the cathode ray beam to a uniform preselected level, a varying current flow is obtained in the return path from the backing plate, which is characteristic or denotative of the electrostatic charge pattern originally present on the dielectric medium. A DC. bias potential may be applied between the backing plate and pin tube to modify or reverse the relation between the current fiow and the electrostatic charge pattern. From this varying return current, one can readily obtain a corresponding voltage output signal suitable for transmission to a remote station, where this resultant time based voltage signal may be reconverted into spatial presentation corresponding to that being sensed from said dielectric medium.

The read-out of electrostatic patterns and conversion thereof to electric current values is accomplished in accordance with another embodiment of the present invention without any discharge between the pins and the adjacent dielectric medium. This is accomplished by scanning the pins in a pin tube with a low velocity electron beam which is selectively reflected back to the cathode in accordance with the pin potentials. A DC. bias potential may also be applied in this embodiment between the backing plate and the cathode to modify or reverse the relation between the return carrier flow and the electirostatic charge pattern. From this varying internal carrier, one can readily obtain a correspond-ing voltage output signal to a remote station. In accordance with this embodiment of the invention, the electrostatic charge pattern will not be destroyed or damaged in the read-out process.

Accordingly, it is one object of the present invention to provide for the transducing of electrostatic information into electrical current form.

Another object of the present invention is to provide for Still another object of the present invention is to provide for the conversion of an electrostatic spatial pattern of information into an electric current signal, the transmission of said information to a remote station, and the reconvension of said information at said remote station into a spatial presentation pattern.

Other objects and advantages of the present invention will become apparent to those skilled in the art from a consideration of the following detailed description of illustrative embodiments of the invention, had in conjunction with the accompanying drawings in which like numerals refer to like or corresponding parts, and wherein:

FIG. 1 is a schematic illustration of one system embodying the present invention;

FIG. 2 is a supplemental schematic illustration of a portion of the sending station in FIG. 1;

FIG. 3 is a supplemental schematic illustration of a portion of the receiving station in F IG. 1;

, FIG. 4 is a schematic illustration of a modified form of sending station in accordance with the present invention; and

FIG. 5 is a schematic illustration of still another form of sending station in accordance with the invention.

The basic system and approach of the present invention is illustrated in FIG. 1, and comprises a sending station and a receiving station 40. At the sending station there is schematically shown a cathode ray pin tube 11 having the usual components of a cathode 13, control grid 13a, accelerating anode 14, deflection plates 15, and

, a line of pins 12 passing through the target plate 12a of tube 11. The cathode ray beam is indicated by the dashed line 16, and this beam is intended to be deflected by plates 15 as indicated by arrow 17 to scan. and impinge upon the line of pins 12 successively. The conventional operating circuitry of the cathode ray tube 11 largely omitted for purposes of clarity, as being well understood by those skilled in the art. A web 18 of dielectric material is locatedopposite the target face 12a of the tube 11 and the exterior ends of pins 12, and is slightly spaced from the ends of these pins to provide an air gap 19. The Web 18 is oriented to travel out of the plane of the drawing in FIG. 1, as is shown in FIG. 2, with the line of travel designated by arrow 25 in FIG. 2. A conductive backing plate or bar 20 is located in contact with the face of web 18 opposite from that adjacent pins 12, and this bar is oriented to extend in line with and immediately opposite to the line of pins 12. Bar 20 is electrically connected to a switch 21, and thence either directly to ground by means ofswitch contact 21b, or through resistor 22 and potentiometer 27 to ground by switch contact 21a. This connection of bar 20 to ground designates a return electrical path to the cathode 12 for the cathode ray beam 16. Potentiometer- 27 is connected to a battery 28 and thus permits the D.-C. potential of backing plate 20 to be adjusted as desired. It is often preferred to adjust the potential on backing plate 20 to a value just below that which would cause discharge between the electrostatic charge pattern and pins 12 if they were at cathode potential. A bypass condensor 29 ensures that a constant A.C. impedance is presented to backing plate 20, regradless of the setting of potentiometer.

Some of the conventional circuitry for operating the pin tube 11 is indicated in block fonn by a synch pulse generator 31, which periodically triggers the scanning sawtooth generator 33. The sawtooth voltage output of generator 33 is applied to deflection plates 15 and functions thereby to cause the cathode ray beam 16 to scan across the pins 12 in accordance with the repetition rate and sawtooth slope established by the synch pulse and sawtooth generators.

The operating parameters of tube 11 are chosen so that when beam 16 impinges on a pin or electrode 12, it creates a charge on that pin sufficient to cause a field discharge between such pin and the dielectric web 18-,

' across the air gap 19. However, web 18 already has an electrostatic information pattern embodied in varying degrees, or in the presence and absence, of electrostatic charges over its surface. This precharge on web 18 controls the amount or intensity of field discharge between an activated pin 12 and the web; and since tube 11 is biased to provide an equal charge on each pin 12 as it is scanned by beam 16, the current flow in the field discharge as each pin 12 is energized is a function of the precharge present on the respective incremental portion of web 18 immediately opposite the momentarily activated pin. The amount of field discharge current flow as each pin 12 is energized is reflected in the current flow in the catho-de ray beam return path from backing bar 20 to ground. Backing bar 20 thus functions as a collector for the field discharge current from each of the pins or electrodes 12.

As a result, for each cycle of scan by beam 16 a varying output voltage is developed across resistor 22 as the pins 12 are successively activated by beam 16, which is characteristic of the information charge pattern (the precharge) originally present across that line on web 18 momentarily located opposite pins 12 during the particular scan cycle.

A transverse view of the read-out apparatus is shown in FIG. 2, and corresponding parts have been similarly numbered. As seen in FIG. 2, the dielectric web 18 feeds from a supply roll 25a in the direction of arrow 25 to a take-up r-oll 25b, driven by a motor 30 and in so doing passes through the air gap 19 between pins 12 of tube 11 and the back up bar 20. Between the supply roll 25a and the read-out pin tube 11, there is located an electrostatic information writer 26. This might conveniently be an alpha-numeric writer as previously suggested, for inscribing an alpha-numeric electrostatic message on web 18.

The output voltage of sending station 10 as derived from resistor 22, along with the scanning synch pulse output of generator 31, may be amplified at 23 and then transmitted by any conventional medium to receiving station 40. The receiving station is shown as comprising a cathode ray pin tube 41 corresponding to tube 11, which cooperates in the same way as tube 11 with a web 48 of dielectric material, provided with a backing bar 50 electrically grounded through switch 51 and contact 51b. The output of the sending station 10 when received at station 40 may be again amplified at 66. The synch pulse is then separated from the information signal at 64, and the information signal is applied to the control grid of tube 41 through switch 65 to control the intensity of charge applied to the pins of tube 41 as the cathode ray beam is caused to scan the pins, while the synch pulse is applied to scanning sawtooth generator 63 which develops a sawtooth output applied to the deflection plates of the tube 41. In this manner, the scanning of the pins of the two tubes are synchronized so that the transmitted information is applied to the pins of tube 41 in the same relationship as it was derived from the pins of tube 11.

A transverse view of the pin tube, dielectric web, and associated equipment for the receiving station 40 is shown in FIG. 3. As there shown, the web 48 moves in the direction of arrow 55 from a supply roll 48a, past the tube and in contact with bar 50 in the air gap between the pins of the tube and the bar, to take-up roll 48b. Before entering the said air gap, the dielectric web 48 is preconditioned at 56-to obtain a uniform electrostatic background charge (or zero charge if desired). As the web is then exposed to the field discharge between the pins and backing bar 50, it is variably electrostatically charged in accordance with the intensity of the field discharge developed at each pin, pursuant to the electrical information received and applied to the control grid of tube 41. The electrostatic information pattern may then be developed into visual form and converted into a permanent record, if desired, by the image developer 57, in accordance with usual xerographic techniques.

It will be observed that in the system of FIG. 1, at

sending station 10, switch 21 is closed to contact 21a, switch 32 is closed, and switch 35 is closed to contact 350. This is the condition of the circuit appropriate for sensing the charge pattern on web 18 and transmitting it. For these purposes, the grid 13a of the tube 11 should be energized with a constant voltage, backing bar 20 should be connected to ground through a resistance, and synch pulse generator 31 should provide the time reference for each scanning cycle. On the other hand, the opposite situation prevails at the receiving station 40. Here switch 65 is closed to contact 65b to place the control grid in circuit with the varying incoming information signals;

switch 51 is closed to contact 51b to contact the backing transducer equipment is used for reading out the electrostatic pattern of information at station 10 as is used for recording it at station 40, the send-receive relation of the two stations can be easily reversed, merely by.

reversing the above-described switch relationships. By closing switch 65 to the constant voltage supply contact 65a, closing switch 62 to put synch pulse generator 61 in the circuit, and by closing switch 51 to output contact 51a, tube 41 is put in condition to sense the electrostatic charge pattern on web 48 and transmit the sensed information as a voltage signal developed across resistor 52, along with the synch pulses obtained from generator 61, through amplifiers 53 and 36 to the synch pulse separator 34 at station 10. Elements 57, 58, and 59 then function the same moreover as did elements 27, 28, and 29 previously. In order to place tube 11 in condition to receive this information and apply it as an electrostatic information pattern to Web 18, switch 35 is closed to information input contact 35b, switch 32 is opened to remove synch pulse generator 31 from the circuit, and switch 21 is closed to contact 2112 to ground the backing bar 20. As shown in FIGS. 2 and 3, the transmitting station is provided with an electrostatic information writer,

of the two stations should be travelling at the same linear speeds. This may be readily accomplished for example merely by the use of synchronous speed motors to drive the two webs.

static charge pattern on the photoconductive layer 72, the charge pattern is moved past read-out tube 73. Similarly as described with reference to FIG. 1, there results a varied field discharge from the pins or electrodes of tube 73 in accordance with the intensity of charge on each incremental area of layer 72 immediately opposite its respective pin. Accordingly, the return current for the cathode ray beam flowing from backing cylinder 71 across resistor 77 to ground varies therewith, and the varying voltage thereby developed across resistor 77 may be amplified at 78 and constitute a tranmsission output which can be reproduced in a spatial display, for example, by the receiving station 40 of FIG. 1. i

In the specific embodiment shown in FIG. 4, during the period of time that the photoconductor layer 72 is being precharged at station 74 and exposed to an optical image at station -75, a read-out signal from station 73 could not I be transmitted, because it would be combined with the Instead of using a dielectric web as the electrostatic I information medium, one may utilize the principles of the present invention in conjunction with a photoconductive medium, as illustrated in FIG. 4. A drum 71 of electrical conducting material is used asthe backing plate or collector for a cylindrical selenium photoconductive layer 72. Positioned circumferentially about the drum are: a read-out station 73, comprising a cathode ray pin tube and associated circuitry corresponding to tube 11 in FIG. 1; a precharge station 74 for applying a uniform electrostatic charge to the surface of the photoconductive layer 72; and an optical image read-in station 75, where the precharged photoconductor 72 is exposed to an optical image, whereby the charge on the surface of photoconductive layer is variably discharged through backing drum 71 to ground in accordance with the light pattern of the image employed. This variable optical discharge of the selenium layer 72 results, of course, from the fact that the layer is rendered variably conductive in' accordance with the light applied thereto to permit the variable conduction of the electrostatic charge therethrough to the backing drum 71..

After the layer 72'is precharged and exposed to an optical image pattern to produce a corresponding electrooverall charge and discharge from the optical image readin operations. Therefore, it is desirable to close switch 76 to the ground contact 76b during the period of precharge of layer 72 and optical image exposure. After these operations the electrostatic record is ready for readout, so that switch 76 may then be closed to the transmit contact 76w for the pin tu-be read-out operation.

FIGURE 5 shows a modified read-out device. It comprises a cathode ray tube 80 which, like that of FIGURE 1, has a set of electrically conductive pins 12 passing through the target plate. A backing plate 20 may similarly be positioned adjacent to the pins and carry an image bearing dielectric sheet or web 18. Backing plate 20 may be biased by meansof a potentiometer 27 and battery 28 in a manner similar to that of FIGURE 1. This type of cathode ray tube is arranged so as to project a very slow electron beam towards pins 12 and substantially perpendicular to the target plate. If the potential of a pin being scanned is more negative than that of cathode 13 the electrode beam will not reach the pin but will instead be reflected to the vicinity of the cathode where it is collected and can be measured. If a pin 12 is less negative than cathode 13 it will accept electrons until it is charged to the potential of the cathode. This charge acceptance obviously reduces the returning electron beam. The initial potential of the pins is, of .course, determined by capacitive coupling to the electrostatic image on web 18 and to the bias potential on backing plate 20.

The electrode beam from cathode 13 is focused by a circular coaxial magnetic focusing coil 87. It is also accelerated toward pins 12 by grids 82 and 83 and is then decelerated by grid 84 before it reaches pins 12. Scanning of the beam is accomplished by a deflection coil 85 in conjunction with sweep circuitry not shown, but comparable to that of FIG. 1. As is well known, electrostatic and magnetic focusing and deflection are to some extent interchangeable in the cathode ray art. The returning electron beam is intercepted by an electrode 86 in the vicinity of the cathode. This electrode is conveniently the first dynode of an electron multiplier 87 which amplifies the returning beam within the cathode ray tube. It will be recognized that the electron optics of this read-out device are substantially similar to that of a conventional image orthicon tube used for example in television broadcasting. Accordingly, it is convenient to use the appropriate elements of a commercial image orthicon tube in constructing the read-out device of this figure. A detailed description of the various electrode and coil structures will not be given since they are well known in the television art. Potentiometer 27 is normally adjusted so that pins 12, in the absence of the electrode beam, are somewhat less negative or more positive than cathode 13. The signal output from the electron multiplier may be transmitted and reproduced in the same manner as shown, for example in connection with FIGURE 1. Unlike the embodiment of FIGURE 1, however, that of FIGURE 5 does not alter or destroy the electrostatic charge pattern.

beam may be scanned in a two dimensional raster by conventional means and a two dimensional array of pins 12 is employed. 7

The foregoing detailed description of the invention is intended merely to facilitate an understanding of the invention, and is not to be construed as a limitation thereon. Obviously numerous modifications, variations, and changes will be apparent to those skilled in the art, and therefore such as are embraced by the spirit and scope of the appended claims are contemplated as within the purview of this invention.

What is claimed is:

1. A system for transmitting information presented in the form of an electrostatic pattern upon a dielectric surface from a first station to a second station, comprising:

(I) .a read-out apparatus at said first station, and a readin apparatus at said second station, said read-out apparatus comprising:

(a) a cathode ray tube having a plurality of electrically conductive pins passing through the target wall,

(b) means to advance the electrostatic charge pat tern past and closely adjacent the ends of said pins lying outside the cathode ray tube,

=(c) means to scan the cathode ray beam across the ends of said pins lying inside the cathode ray tube,

-(d) means to develop an electrical output signal in 'synchronism with the scanning of the pins by the cathode ray beam and having an instantaneous magnitude proportional to the potential difference between the pin being scanned and that portion of the electrostatic pattern opposite said pin depending on the magnitude of the portion of the electrostatic charge pattern opposite the pin being scanned,

(11) said read-in apparatus comprising:

(a) means for receiving said output signal,

(b) a cathode ray tube having a plurality of electrically conductive pins passing through the target wall,

(c) means to advance a charge receptive dielectric material past and closely adjacent the ends of said pins lying outside the cathode ray tube,

(d) means to scan the cathode ray beam across the ends of said pins lying inside the cathode ray tube in synchronism with the scanning beam in said read-out apparatus, and

(e) means to intensity modulate the cathode ray beam in accordance with said received output signal thereby forming on said dielectric medium an electrostatic charge pattern corresponding to said original electrostatic charge pattern.

2. A system according to claim 1 wherein said cathode ray beam of the read-out apparatus is of sufficient intensity to effect electrical discharges between the said conductive pins and the said electrostatic pattern, and wherein said means to develop an electrical output signal comprises a conductive element positioned behind the said dielectric surface.

3. A system according to claim 2 further including means to apply a bias potential to the conductive element.

References Cited by the Examiner UNITED STATES PATENTS 3,040,124 6/1962 Camras 178-6.6

DAVID G. REDINBAUGH, Primary Examiner.

H. W. BRITTON, Assistant Examiner. 

1. A SYSTEM FOR TRANSMITTING INFORMATION REPRESENTED IN THE FORM OF AN ELECTROSTATIC PATTERN UPON A DIELECTRIC SURFACE FROM A FIRST STATION TO A SECOND STATION, COMPRISING: (I) A READ-OUT APPARATUS AT SAID FIRST STATION, AND A READIN APPARATUS AT SAID SECOND STATION, SAID READ-OUT APPARATUS COMPRISING: (A) A CATHODE RAY TUBE HAVING A PLURALITY OF ELECTRICALLY CONDUCTIVE PIN PASSING THROUGH THE TARGET WALL, (B) MEANS TO ADVANCE THE ELECTROSTATIC CHARGE PATTERN PAST AND CLOSELY ADJACENT THE ENDS OF SAID PINS LYING OUTSIDE THE CATHODE RAY TUBE, (C) MEANS TO SCAN THE CATHODE RAY BEAM ACROSS THE ENDS OF SAID PINS LYING INSIDE THE CATHODE RAY TUBE, (D) MEANS TO DEVELOP AN ELECTRICAL OUTPUT SIGNAL IN SYNCHRONISM WITH THE SCANNING OF THE PINS BY THE CATHODE RAY BEAM AND HAVING AN INSTANTANEOUS MAGNITUDE PROPORTIONAL TO THE POTENTIAL DIFFERENCE BETWEEN THE PIN BEING SCANNED AND THAT PORTION OF THE ELECTROSTATIC PATTERN OPPOSITE SAID PIN DEPENDING ON THE MAGNITUDE OF THE PORTION OF THE ELECTROSTATIC CHARGE PATTERN OPPOSITE THE PIN BEING SCANNED, (II) SAID READ-IN APPARATUS COMPRISING: (A) MEANS FOR RECEIVING SAID OUTPUT SIGNAL, (B) A CATHODE RAY TUBE HAVING A PLURALITY OF ELECTRICALLY CONDUCTIVE PINS PASSING THROUGH THE TARGET WALL, (C) MEANS TO ADVANCE A CHARGE RECEPTIVE DIELECTRIC MATERIAL PAST AND CLOSELY ADJACENT THE ENDS OF SAID PINS LYING OUTSIDE THE CATHODE RAY TUBE, (D) MEANS TO SCAN THE CATHODE RAY BEAM ACROSS THE ENDS OF SAID PINS LYING INSIDE THE CATHODE RAY TUBE IN SYNCHRONISM WITH THE SCANNING BEAM IN SAID READ-OUT APPARATUS, AND (E) MEANS TO INTENSITY MODULATE THE CATHODE RAY BEAM IN ACCORDANCE WITH SAID RECEIVED OUTPUT SIGNAL THEREBY FORMING ON SAID DIELECTRIC MEDIUM AN ELECTROSTATIC CHARGE PATTERN CORRESPONDING TO SAID ORIGINAL ELECTROSTATIC CHARGE PATTERN. 